Naturally occurring deposits containing oil and natural gas are located throughout the world. Given the porous and permeable nature of the subterranean structure, it is possible to bore into the earth and set up a well where oil and natural gas are pumped out of the deposit. These wells are large, costly structures that are typically fixed at one location. As is often the case, a well may initially be very productive, with the oil and natural gas being pumpable with relative ease. As the oil or natural gas near the well bore is removed from the deposit, other oil and natural gas may flow to the area near the well bore so that it may be pumped as well. However, as a well ages, and sometimes merely as a consequence of the subterranean geology surrounding the well bore, the more remote oil and natural gas may have difficulty flowing to the well bore, thereby reducing the productivity of the well.
To address this problem and to increase the flow of oil and natural gas to the well bore, a technique may be employed of fracturing the subterranean area around the well to create more paths for the oil and natural gas to flow toward the well bore. This fracturing may be performed by hydraulically injecting a fracturing fluid at high pressure into the area surrounding the well bore. This fracturing fluid is thereafter removed from the fracture to the extent possible so that it does not impede the flow of oil or natural gas back to the well bore. Once the fracturing fluid is removed, however, the fractures may tend to collapse due to the high compaction pressures experienced at well-depths, which may exceed 20,000 feet.
To reduce the likelihood of the fractures closing, a propping agent, also known as a “proppant” or “anti-flowback additive,” may be included in the fracturing fluid, so that as much of the fracturing fluid as possible may be removed from the fractures while leaving the proppant behind to hold the fractures open. As used in this application, the term “proppant” refers to any non-liquid material that is present in a proppant pack (a plurality of proppant particles) and provides structural support in a propped fracture. “Anti-flowback additive” refers to any material that is present in a proppant pack and reduces the flowback of proppant particles but still allows for production of oil at desired rates. The terms “proppant” and “anti-flowback additive” are not necessarily mutually exclusive, so a single particle type may meet both definitions. For example, a proppant particle may provide structural support in a fracture, and it may also be shaped to have anti-flowback properties, allowing it to meet both definitions.
Because there may be extremely high closing pressures in fractures, it may be desirable to provide proppants and anti-flowback additives that have a high crush resistance. For example, the useful life of the well may be shortened if the proppant particles break down, allowing the fractures to collapse and/or clog with “fines” created by the broken-down proppant particles. For this reason, it may be desirable to provide proppants that are resistant to breakage, even under high crush pressures.
In addition, it may also be desirable to provide a proppant or anti-flowback additive that packs well with other proppant particles and the surrounding geological features, so that the nature of this packing of particles does not unduly impede the flow of the oil and natural gas through the fractures. For example, if the proppant particles become too tightly packed and create low porosity, they may actually inhibit the flow of the oil or natural gas to the well bore rather than increase it.
The nature of the packing may also affect the overall turbulence generated as the oil or natural gas flows through the fractures. Too much turbulence may increase the flowback of the proppant particles from the fractures toward the well bore, which may undesirably decrease the flow of oil and natural gas, contaminate the well, cause abrasion to the equipment in the well, and/or increase the production cost as the proppants that flow back toward the well must be removed from the oil and natural gas. In addition, too much turbulence may also increase a non-Darcy flow effect, which may ultimately result in decreased conductivity.
As resources become more scarce, the search for oil and natural gas may involve penetration into deeper geological formations, and the recovery of the such resources may become increasingly difficult. Therefore, there may be a desire to provide proppants and anti-flowback additives that have an excellent conductivity and permeability under extreme conditions. In addition, there may be a desire to provide proppants and anti-flowback additives formed from less costly or more prevalent materials that still provide one or more desirable characteristics for propping fractures in modern wells.